An important problem in cassette tape recorders relates to size-reduction and thickness-reduction. The size-reduction and thickness-reduction greatly depend upon the configuration and structure of the cabinet of the cassette tape recorder, commensurate with the layout of parts to be encased therein. FIG. 1 is a cross-sectional view of a conventional cassette tape recorder comprising an upper cabinet part 3 and a lower cabinet part 4 which are combined with each other so as to encase a mechanism base plate 1 for keeping a tape cassette 2 thereon and driving a tape in the tape cassette 2 in connection with a magnetic head 5. As obvious from the same figure, this arrangement creates a relatively large space A because the tape cassette 2 has convex portions 6 at its front side. One conceivable solution is to form the upper cabinet 3 along a surface of the tape cassette 2 as illustrated in FIG. 2. However, this design consideration may result in lack of fit when put in a pocket of a user's dress for carrying thereby.